Arctic offshore platform

Abstract

An offshore structure for use in drilling and producing wells in arctic regions having a conical shaped lower portion that extends above the surface of the water and a cylindrical upper section. The conical portion is provided with a controlled stiffness outer surface for withstanding the loads produced by ice striking the structure. The stiffness properties of the outer shell and flexible members are designed to distribute the load and avoid high local loads on the inner parts of the structure.

What is claimed is: 
     
       1. An offshore structure for use in arctic water containing moving ice masses comprising: a frustum base section and a circular upper section, said base section having sufficient height to extend above the surface of the water;   the skin of said frustum section having a controlled stiffness cellular structure formed by an outer plate member and an inner plate member, said outer and inner plate members being separated by a series of radial and meridional webs fastened to said plates to form a cellular structure; and   a flexible beam structure, said beam structure being formed by a series of circumferential beams supported by a series of radial bulkheads projecting upward from the bottom of said frustum, said skin being attached to said flexible beam structure intermediate said radial bulkheads.   
     
     
       2. A frusto-conical base member for use in an offshore structure for conducting operations in arctic waters having moving ice, said base member comprising: a solid circular bottom;   an outer skin for said base, said outer skin being formed by a solid outer plate and a solid inner plate, said inner and outer plates having a general conical shape and radially spaced, a plurality of meridional web members positioned between said inner and outer plates and fasten thereto to maintain the spacing between said plates;   a plurality of radial bulkheads attached to said bottom and terminating short of said outer skin; and   a plurality of horizontal flexible beams, said beams being secured between said radial bulkheads to form a series of vertically spaced substantially circular beams, said beams supporting said outer skin at points intermediate said bulkheads.   
     
     
       3. The base member of claim 2 wherein in addition to said meridional members a series of circumferential webs are positioned between said inner and outer plates and fastened thereto. 
     
     
       4. The base member of claim 3 and in addition secondary stiffening webs, said webs being attached to the outer shell and positioned between said meridional members. 
     
     
       5. The base of claim 4 wherein said inner plate is provided with a series of load transfer boxes that project inwardly from said inner plate, said load transfer boxes having a flat surface that contacts said beams at approximately the center thereof. 
     
     
       6. The base member of claim 5 wherein said box has a parallelogram cross section.